The present invention is concerned with combustion and heat transfer processes and apparatus. The invention has general applicability in the fields of combustion and heat transfer and is applicable to industrial and non-industrial processes as well as residential use. Practical industrial application of the invention may be found in the field of steam generation for heating and for electrical power generation. In addition, non-industrial applications of the invention include cooking appliances, stoves, water heaters, furnaces and the like.
Efficient use of heat generated from a fuel involves two fundamental steps. This first is the combustion of the fuel, and the second is the heat transfer from the products of combustion to the desired heat sink. Combustion processes are carried out so that the ambient temperature in the combustion area is extremely high, i.e., typically greater than 1500xc2x0 C. It is well known that at high temperatures, nitrogen present in fuel and air reacts with oxygen to forms various oxides, commonly referred to as NOx. The generation of NOx increases with the temperature, especially when an excess of oxygen is present. It is therefore desirable, when dealing with combustion of fuel, to maintain temperatures as low as possible to inhibit the formation of pollutants like NOx. An alternative is to reduce the concentration of oxygen below the stoichiometric requirement.
In many areas of the world, wood is still used as the main fuel for cooking. This is particularly true for so-called lesser-developed countries where access to other fuels may not be readily available, or affordable.
To inhibit the formation of pollutants during combustion, and to efficiently utilize available fuels, it is desirable to develop appliances in which there is efficient combustion of the fuel and simultaneous efficient heat transfer of the heat generated during the combustion process to an appropriate heat sink.
In accordance with the invention, there is provided a heating apparatus comprising a housing having a general axis. The apparatus further comprises a fuel support surface. The apparatus comprises a plurality of air injectors arranged on the support surface. The air injectors have a plurality of apertures to deliver air in a first direction substantially parallel to the axis of the housing and in a second direction substantially normal to the axis of the housing. Fuel is burned adjacent the fuel support surface. Air is injected with a fan from an air inlet chamber to the air injectors. In addition, the heating apparatus preferably comprises a restrictor ring placed within the housing above the fuel support surface to restrict the cross-sectional area of the housing adjacent the restrictor ring. Further, the apparatus comprises a support means for supporting a heat sink adjacent the upper portion of the combustion chamber. There is a thermal transfer gap between the upper edge of the combustion chamber and the lower edge of the heat sink so that gases passing upwardly through the housing impinge upon the heat sink and pass through the thermal transfer gap after transferring the heat contained therein to the heat sink.